As is also disclosed in U.S. Pat. No. 4,538,483, U.S. Pat. No. 5,305,666 and Japanese Patent Publication No. H06-155319, a fastening member comprising a pin having a hole on the tip end surface thereof for engaging with a tool, and nut that is screwed on to the pin is used. Such a fastening member is illustrated in FIG. 9.
As illustrated in FIG. 9, the fastening member comprises a pin 50 and nut 60. The pin 50 comprises a head section 51 and a shaft section 52. Male screw threads 53 are formed around the surface of the shaft section 52, and a tool engagement hole 54 is formed on the tip end surface of the shaft section 52. The tool engagement hole 54 is a hexagonal hole and a hexagonal wrench engages with the tool engagement hole 54.
The nut 60 comprises a female thread section 61 that screws onto the male thread section 53, and a tool engagement section 63 having an outer perimeter shape that engages with a fastening tool such as a wrench, the female thread section 61 and the tool engagement section 63 being connected via a weak section 62 that could be fractured by a shear force. This weak section 62 is achieved by having a smaller cross-sectional area than the female thread section 61 and tool engagement section 63, with this weak section 62 fracturing by applying a torque between the female thread section 61 and tool engagement section 63, and as a result, the tool engagement section 63 separates from the female thread section 61. The female thread section 61 remains screwed and fastened to the pin 50.
The simplest construction of a fastening tool for performing the fastening work of the fastening tool above is a key wrench that engages with the tool engagement hole 54 of the pin 50 and a wrench that engages with the tool engagement section 63 of the nut 60. However, a condition of this tool is that the key wrench that engages with the pin 50 does not interfere with the wrench that engages with the nut 60. In other words, the wrench that engages with the nut 60 has an engagement section that is open such as an open-end wrench, or in the case of a socket wrench, a through hole through which the key wrench passes is necessary.
By relatively rotating both of these wrenches, it is possible to perform fastening work by screwing together the engaged pin 50 and nut 60.
Instead of the simple key wrench and socket wrench being separate tools, a fastening tool having construction in which both of these wrenches are rearranged and integrated is also used (U.S. Pat. No. 4,538,483, U.S. Pat. No. 5,305,666, Japanese Patent Publication No. H06-155319).
A power-driven tool is disclosed in U.S. Pat. No. 4,538,483, a power-driven and manual tool is disclosed in U.S. Pat. No. 5,305,666, and a manual tool is disclosed in Japanese Patent Publication No. H06-155319.
Each of these tools has a socket wrench that engages with the nut (60) and a key wrench that engages with the pin (50 in FIG. 9 of this specification) or a part that holds the key wrench.
The manual tool disclosed in Japanese Patent Publication No. H06-155319 has basic construction of a combination of a ratchet, socket wrench, and an L-type key wrench. Using a commercially available wrench is as the L-type key wrench, the long end of the wrench must be inserted inside the ratchet and socket wrench. Therefore, the portion of the wrench which is held by hand is short, making it difficult to apply force to the L-type key wrench. In order to perform work comfortably, a separate special tool is necessary.
The portion of the L-type key wrench that is inserted inside the ratchet and socket wrench is not held so as not to rotate during the work. Therefore, when performing fastening work, torsion stress occurs along the entire length of the L-type key wrench, and the amount of torsional deformation could be large.
In the power-driven tool that is disclosed in U.S. Pat. No. 4,538,483 and U.S. Pat. No. 5,305,666, the hexagonal shaped tip end part that engages with the pin (36 in U.S. Pat. No. 4,538,483, 114 in U.S. Pat. No. 5,305,666) is inserted in a hexagonal hole of a cylindrical part (38 in U.S. Pat. No. 4,538,483, 98 in U.S. Pat. No. 5,305,666) and held such that it cannot rotate. This cylindrical part passes through the tip portion of a nut runner, which turns the nut with power, and protrudes out the opposite side, and is restrained by a spring (66 in U.S. Pat. No. 4,538,483, 138 in U.S. Pat. No. 5,305,666) such that it can move in the axial direction, but cannot rotate. The reason that this cylindrical part is capable of moving in the axial direction with respect to the nut runner is that as the pin and nut are screwed and rotated in the tightening direction, the tip end part that engages with the pin must move back with respect to the pin and nut runner. The reason that this cylindrical part is restrained such that it cannot rotate with respect to the frame (non-rotating part) of the nut runner is that when rotating the nut, the pin is fixed so that it does not rotate with the nut.
Naturally, in the tool disclosed in U.S. Pat. No. 4,538,483 and U.S. Pat. No. 5,305,666, a special tool, which includes the hexagonal tip end part that engages with the pin, becomes necessary.
However, even with the conventional technology above, there were further problems such as below. The tip end part that engages with the pin and the cylindrical part that supports this such that it cannot turn are integrated and move in the axial direction together. Therefore, regardless of the progressive stage of the fastening work, the distance between the location of the tip end that receives torque from the pin of this tip end part, and the location where the tip end part is supported by the cylindrical part so that it cannot turn does not change. Therefore, in the last half of the fastening work, particularly in the stage of twisting off the nut, even when a large torque load is applied to the tip end part that engages with the pin, torsional stress occurs along the length in the axial direction as at the start of the fastening work, so naturally the amount of torsional deformation becomes large.
In other words, in the conventional technology, it is not possible to employ construction of firmly holding the tip end part that engages with the pin at a closer location to the pin.
As disclosed in U.S. Pat. No. 4,538,483, even in the case of construction in which the tip end part of the cylindrical part (38 in U.S. Pat. No. 4,538,483) is inserted into the nut at the start of the fastening work, as the fastening work proceeds, this cylindrical part moves back and comes out from inside the nut, and because this cylindrical part is formed such that it is thin enough to be inserted in the nut, it cannot display sufficient torsional rigidity. Therefore, it is not possible to employ construction in which the tip end part that engages with the pin is firmly held at a location closer to the pin.
As the amount of torsional deformation of the tip end part that engages with the pin becomes large, the strain that occurs at the location where the tip end part engages with the pin becomes large, so the possibility that the engagement between the tip end part and the pin will be lost becomes high. Therefore, by the tip end part scraping the inside of the tool engagement hole, there is a possibility that the engagement will gradually become insufficient, and there is also a possibility that twisting off the nut will become impossible.
Moreover, in the power-driven tool disclosed in U.S. Pat. No. 4,538,483 and U.S. Pat. No. 5,305,666, the tip end part that engages with the pin and the cylindrical part that holds the tip end part are held such that they cannot rotate with respect to the frame (non-rotating part) of the nut runner, so in order to find the angle at which the tip end part engages with the tool engagement hole of the pin, the entire nut runner that includes said mounted tools must be rotated around the pin shaft. The weight of the nut runner is large and engages with the nut via a socket wrench. Therefore, it is difficult to know by feeling of the hand whether or not the tip end part is engaged with the tool engagement hole of the pin.